The present application is based on Japanese Application 2000-109827, filed Apr. 11, 2000, which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to methods for continuously manufacturing low-oxygen copper, having a suppressed oxygen content, by continuously casting molten copper produced in a melting furnace.
2. Description of the Background
Low-oxygen copper (called xe2x80x9coxygen-free copperxe2x80x9d in some cases) in which the content of oxygen is controlled to 20 ppm or less, and more preferably, to 1 to 10 ppm, is widely used for producing various shapes, e.g., ingot forms such as billets and cakes, rolled sheets, wires and cut forms. As a method for manufacturing low-oxygen copper, molten copper is produced in a high-frequency furnace such as a channel furnace or a coreless furnace, the molten copper is transferred to a continuous casting machine while held in an airtight atmosphere, and the casting is then performed.
When low-oxygen copper is produced by using a high-frequency furnace as described above, there are advantages in that a higher temperature can be easily obtained by a simple operation and the qualities of the products are very uniform since no chemical reaction occurs in production of the molten copper. However there are disadvantages in that the construction cost and the operating cost are high, and productivity is low.
In order to carry out mass production of low-oxygen copper at lower cost, a method using a gas furnace, such as a shaft kiln, is preferably employed. However, when such a gas furnace is used, since combustion is performed in the furnace, oxidation occurs and the oxidized molten copper must be processed by a reducing treatment. This disadvantage of the gas furnace is not observed when a high-frequency furnace is used. As a result, low-oxygen copper cannot be produced unless the amount of oxygen contained in the molten copper is reduced by using a reducing gas and/or an inert gas in a step of transferring the molten copper before the molten copper is fed to a continuous casting machine.
In addition, even when such a deoxidizing step is performed, holes will be formed in the low-oxygen copper and may result in defects such as blisters in some cases. In the case described above, the quality of the low-oxygen copper is degraded. In particular, when a copper wire is manufactured, the holes will cause defects in a rolling step, and hence the copper wire has poor surface qualities. Accordingly, it is generally believed that production of high quality low-oxide copper is difficult to perform using a gas furnace, and hence most low-oxide copper is produced using a high-frequency furnace.
The holes described above are formed by bubbles of steam (H2O) produced by combination of hydrogen and oxygen, due to the decease in solubility of the gases in the molten copper when it is solidified. The bubbles are trapped in the molten copper in cooling and solidification and remain in the low-oxide copper, and hence holes are generated. From a thermodynamic point of view, the concentrations of hydrogen and oxygen in molten copper can be represented by the equation shown below.
[H]2[O]=pH2OKxe2x80x83xe2x80x83Equation (A) 
In the equation (A), [H] represents the concentration of hydrogen in the molten copper, [O] represents the concentration of oxygen in the molten copper, pH2O represents a partial pressure of steam in the ambience, and K represents an equilibrium constant.
Since the equilibrium constant K is a function of temperature and is constant at a constant temperature, the concentration of oxygen in the molten copper is inversely proportional to the concentration of hydrogen. Accordingly, in accordance with the equation (A), the concentration of hydrogen is increased by performing a deoxidizing treatment by reduction, and as a result, holes are easily generated during solidification, whereby only an ingot of low-oxygen copper having poor quality can be manufactured.
On the other hand, molten copper containing hydrogen at a low concentration can be obtained by melting copper in a state near complete combustion using an oxidation-reduction method, which is a general degassing method. However, in a subsequent deoxidizing step, a long moving distance of the molten copper must be ensured, and hence, the method described above cannot be practically used.
In consideration of the problems described above, an object of the present invention is to provide an apparatus for manufacturing low-oxide copper, in which a dehydrogenating treatment can be performed without requiring a long moving distance of molten copper, the generation of holes in solidification is suppressed, and high quality low-oxide copper can be obtained, having superior surface quality.
An apparatus for continuously manufacturing ingots of low-oxygen copper according to the present invention comprises a melting furnace in which combustion is performed in a reducing atmosphere so as to produce molten copper; a soaking furnace for maintaining a predetermined temperature of the molten copper supplied from the melting furnace; a casting trough for sealing the molten copper supplied from the soaking furnace in a non-oxidizing atmosphere and for transferring the molten copper to a turn-dish; a degasser provided in the casting trough for dehydrogenating the molten copper passing through the casting trough; a continuous casting machine for continuously producing cast copper from the molten copper supplied from the turn-dish; and a cutter for cutting the cast copper into a predetermined length.
An apparatus for continuously manufacturing ingots of low-oxygen copper according to the present invention comprises a melting furnace in which combustion is performed in a reducing atmosphere so as to produce molten copper; a holding furnace for maintaining a predetermined temperature of the molten copper supplied from the melting furnace; a casting trough for sealing the molten copper supplied from the holding furnace in a non-oxidizing atmosphere and for transferring the molten copper to a tundish; a degasser provided in the casting trough for dehydrogenating die molten copper passing through the casting trough; a continuous casting machine for continuously producing cast copper from the molten copper supplied from the tundish; and a cutter for cutting the cast copper into a predetermined length.
In the apparatus for manufacturing ingots of low-oxygen copper described above, the stirrer comprises dikes causing a meandering of the flow path of the molten copper passing through the casting trough.
An apparatus for continuously manufacturing a low-oxygen copper wire according to the present invention comprises a melting furnace in which combustion is performed in a reducing atmosphere so as to produce molten copper; a soaking furnace for maintaining a predetermined temperature of the molten copper supplied from the melting furnace; a casting trough for sealing the molten copper supplied from the soaking furnace in a non-oxidizing atmosphere and for transferring the molten copper to a turn-dish; a degasser provided in the casting trough for dehydrogenating the molten copper passing through the casting trough; a belt caster type continuous casting machine for continuously producing cast copper from the molten copper supplied from the turn-dish; and a rolling machine for rolling the cast copper so as to produce the low-oxygen copper wire.
An apparatus for continuously manufacturing a low-oxygen copper wire according to the present invention comprises a melting furnace in which combustion is performed in a reducing atmosphere so as to produce molten copper; a holding furnace for maintaining a predetermined temperature of the molten copper supplied from the melting furnace; a casting trough for sealing the molten copper supplied from the holding furnace in a non-oxidizing atmosphere and for transferring the molten copper to a tundish; a degasser provided in the casting trough for dehydrogenating the molten copper passing through the casting trough; a belt caster type continuous casting machine for continuously producing cast copper from the molten copper supplied from the tundish; and a rolling machine for rolling the cast copper so as to produce the low-oxygen copper wire.
In the apparatus for manufacturing a low-oxygen copper wire described above, the stirrer comprises dikes causing a meandering of the flow path of the molten copper passing through the casting trough.
An apparatus for continuously manufacturing a wire composed of a low-oxygen copper alloy according to the present invention comprises a melting furnace in which combustion is performed in a reducing atmosphere so as to produce molten copper; a soaking furnace for maintaining a predetermined temperature of the molten copper supplied from the melting furnace; a casting trough for sealing the molten copper supplied from the soaking furnace in a non-oxidizing atmosphere and for transferring the molten copper to a turn-dish; a degasser provided in the casting trough for dehydrogenating the molten copper passing through the casting trough; an adder for adding silver to the dehydrogenated molten copper; a belt caster type continuous casting machine for continuously producing cast copper alloy from the molten copper supplied from the turn-dish; and a rolling machine for rolling the cast copper alloy so as to produce the wire composed of the low-oxygen copper alloy.
An apparatus for continuously manufacturing a wire composed of a low-oxygen copper alloy according to the present invention comprises a melting furnace in which combustion is performed in a reducing atmosphere so as to produce molten copper; a holding furnace for maintaining a predetermined temperature of the molten copper supplied from the melting furnace; a casting trough for sealing the molten copper supplied from the holding furnace in a non-oxidizing atmosphere and for transferring the molten copper to a tundish; a degasser provided in the casting trough for dehydrogenating the molten copper passing through the casting trough; an adder for adding silver to the dehydrogenated molten copper; a belt caster type continuous casting machine for continuously producing cast copper alloy from the molten copper supplied from the tundish; and a rolling machine for rolling the cast copper alloy so as to produce the wire composed of the low-oxygen copper alloy.
In the apparatus for manufacturing a wire composed of a low-oxygen copper alloy described above, the stirrer comprises dikes for causing meandering of the flow path of the molten copper passing through the casting trough.
An apparatus for continuously manufacturing a base low-oxygen copper material containing phosphorus for use in copper plating according to the present invention comprises a melting furnace in which combustion is performed in a reducing atmosphere so as to produce molten copper; a soaking furnace for maintaining a predetermined temperature of the molten copper supplied from the melting furnace; a casting trough for sealing the molten copper supplied from the soaking furnace in a non-oxidizing atmosphere and for transferring the molten copper to a turn-dish; a degasser provided in the casting trough for dehydrogenating the molten copper passing through the casting trough; an adder for adding phosphorus to the dehydrogenated molten copper; a belt caster type continuous casting machine for continuously producing cast base copper material from the molten copper supplied from the turn-dish; and a rolling machine for rolling the cast base copper material so as to produce the base low-oxygen copper material containing phosphorus for use in copper plating.
An apparatus for continuously manufacturing a base low-oxygen copper material containing phosphorus for use in copper plating according to the present invention comprises a melting furnace in which combustion is performed in a reducing atmosphere so as to produce molten copper; a holding furnace for maintaining a predetermined temperature of the molten copper supplied from the melting furnace; a casting trough for sealing the molten copper supplied from the holding furnace in a non-oxidizing atmosphere and for transferring the molten copper to a tundish; a degasser provided in the casting trough for dehydrogenating the molten copper passing through the casting trough; an adder for adding phosphorus to the dehydrogenated molten copper; a belt caster type continuous casting machine for continuously producing cast base copper material from the molten copper supplied from the tundish; and a rolling machine for rolling the cast base copper material so as to produce the base low-oxygen copper material containing phosphorus for use in copper plating.
In the apparatus for manufacturing a base low-oxygen copper material described above, the stirrer comprises dikes causing a meandering of the flow path of the molten copper passing through the casting trough.
The apparatus for manufacturing a base low-oxygen copper material described above further comprises a cutter for cutting the base low-oxygen copper material rolled by the rolling machine into a predetermined length.
The apparatus for manufacturing a base low-oxygen copper material described above further comprises a washer for washing the base low-oxygen copper material having a predetermined length obtained by using the cutter described above.
In the apparatuses for manufacturing the low-oxygen copper described above, the combustion is performed in a melting furnace in a reducing atmosphere, and hence, the molten copper is deoxidized. The deoxidized copper is sealed in a non-oxidizing atmosphere in the casting trough and is then transferred to the turn-dish. Since the concentration of oxygen is inversely proportional to the concentration of hydrogen as described above, the concentration of hydrogen is increased in the molten copper deoxidized in the melting furnace. When the molten copper passes through the casting trough, while containing hydrogen at a high concentration, dehydrogenation is performed by the degasser. Accordingly, the amount of gas evolved in casting is decreased, the generation of holes in a cast copper is suppressed, and as a result, the defects on the surface of the low-oxygen copper are reduced.
In the apparatuses for manufacturing the low-oxygen copper described above, the combustion is performed in a melting furnace in a reducing atmosphere, and hence, the molten copper is deoxidized. The deoxidized copper is sealed in a non-oxidizing atmosphere in the casting trough and is then transferred to the tundish. Since the concentration of oxygen is inversely proportional to the concentration of hydrogen as described above, the concentration of hydrogen is increased in the molten copper deoxidized in the melting furnace. When the molten copper passes through the casting trough, while containing hydrogen at a high concentration, dehydrogenation is performed by the degasser. Accordingly, the amount of gas evolved in casting is decreased, the generation of holes in a cast copper is suppressed, and as a result, the defects on the surface of the low-oxygen copper are reduced.
In addition, when the molten copper is stirred by the degasser, the hydrogen contained in the molten copper is forced out therefrom, whereby dehydrogenation can be performed. That is, since the molten copper stirrer is provided in the casting trough, the molten copper contacting the stirrer is stirred before it reaches the tundish, and as a result the molten copper is well brought into contact with an inert gas blown into the casting trough for forming a non-oxidizing atmosphere. In the step described above, since a partial pressure of hydrogen in the inert gas is very low compared to that in the molten copper, the hydrogen in the molten copper is absorbed in the non-oxidizing atmosphere formed by the inert gas, whereby dehydrogenation of the molten copper can be performed.
In the case described above, the dike provided in the flow path for the molten copper is preferably in the form of a bar, a plate or the like. In addition, a plurality of dikes may be provided along the flow direction of the molten copper or in the direction perpendicular thereto. Furthermore, when dikes are formed of, for example, carbon, the deoxidizing treatment can also be performed efficiently due to the contact between the molten copper and the carbon.